AC Output Power

AC OUTPUT POWER

Advantages

1. Higher efficiency than class A amplifier

2. Even harmonics are cancelled, so harmonic distortion is minimum.

3. Ripples in supply voltage are eliminated.

4. Zero power dissipation under quiescent conditions

5. Impedance matching is possible.

Disadvantages

1. Two centre tapped transformers are required.

2. Bulky circuit and expensive.

3. Poor frequency response.

4. Cross over distortion is present

CLASS B COMPLEMENTARY SYMMETRY AMPLIFIERS

Fig.5.16 shows the circuit diagram of complementary symmetry class B amplifier. Construction

The circuit uses two transistors one is NPN and other is PNP. It is a transformer less circuit. Symmetry indicates that biasing resistors are equal. The two transistors Q₁ and Q₂ are connected in emitter follower configuration for better impedance matching.

Operation

For positive half cycle of input, Q₁ is ON and in active region and Q₂ is OFF and in cutoff region.

For negative half cycle, Q₂ is ON and Q₁ is OFF. Thus for a complete input cycle, output is as shown in Figure 5.16. In complementary symmetry amplifiers, there is no output transformer as in push pull amplifier.

Advantage

1. The circuit is transformer less. So the weight and cost are less.

2. Impedance matching due to emitter follower configuration.

3. Good Frequency response.

4. Efficiency better than push pull amplifier.

Disadvantage

1. Requires two separate voltage supplies

2. Cross over distortion occurs

3. Requires matching between transistors Q₁ and Q₂.

COMPARISON OF PUSH PULL AND COMPLEMENTARY SYMMETRY AMPLIFIER